<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>微信登录</title>
  </head>

  <body>
    <script>
      var GWC = {
        version: '1.2.0',
        urlParams: {},
        appendParams: function (url, params) {
                if (params) {
                    var baseWithSearch = url.split('#')[0];
                    var hash = window.location.hash.split('#')[1];
                    if (hash) {
                      baseWithSearch = baseWithSearch + '#' + hash;
                    } 
                    for (var key in params) {
                        var attrValue = params[key];
                        if (attrValue !== undefined) {
                            var newParam = key + "=" + attrValue;
                            if (baseWithSearch.indexOf('?') > 0) {
                                var oldParamReg = new RegExp('^' + key + '=[-%.!~*\'\(\)\\w]*', 'g');
                                if (oldParamReg.test(baseWithSearch)) {
                                    baseWithSearch = baseWithSearch.replace(oldParamReg, newParam);
                                } else {
                                    baseWithSearch += "&" + newParam;
                                }
                            } else {
                                baseWithSearch += "?" + newParam;
                            }
                        }
                    }
                }
               
                return baseWithSearch;
            
            },
        getUrlParams: function() {
          var pairs = location.search.substring(1).split('&')
          for (var i = 0; i < pairs.length; i++) {
            var pos = pairs[i].indexOf('=')
            if (pos === -1) {
              continue
            }
            GWC.urlParams[pairs[i].substring(0, pos)] = decodeURIComponent(pairs[i].substring(pos + 1))
          }
        },
        doRedirect: function() {
          var code = GWC.urlParams['code']
          var appId = GWC.urlParams['appid']
          var scope = GWC.urlParams['scope'] || 'snsapi_base'
          var state = GWC.urlParams['state']
          var isMp = GWC.urlParams['isMp'] //isMp为true时使用开放平台作授权登录，false为网页扫码登录
          var baseUrl
          var redirectUri

          if (!code) {
            baseUrl = 'https://open.weixin.qq.com/connect/oauth2/authorize#wechat_redirect'
            if (scope == 'snsapi_login' && !isMp) {
              baseUrl = 'https://open.weixin.qq.com/connect/qrconnect'
            }

            //第一步，没有拿到code，跳转至微信授权页面获取code
            redirectUri = GWC.appendParams(baseUrl, {
              appid: appId,
              redirect_uri: encodeURIComponent(location.href),
              response_type: 'code',
              scope: scope,
              state: encodeURIComponent(state)
            })
        
          } else {
            const params = Object.assign({}, GWC.urlParams)
            delete params.backUrl
            //第二步，从微信授权页面跳转回来，已经获取到了code，再次跳转到实际所需页面
            redirectUri = GWC.appendParams(GWC.urlParams['backUrl'], params)
          }

          location.href = redirectUri
        }
      }

      GWC.getUrlParams()
      GWC.doRedirect()
    </script>
  </body>
</html>
